Constraining First-Order Phase Transitions with Curvature Perturbations

The randomness of the quantum tunneling process induces superhorizon curvature perturbations during cosmological first-order phase transitions. We for the first time utilize curvature perturbations to constrain the phase transition parameters, and find that the observations of the cosmic microwave background spectrum distortion and the ultracompact minihalo abundance can give strict constraints on the phase transitions below 100 GeV, especially for the low-scale phase transitions and some electroweak phase transitions. The current constraints on the phase transition parameters are largely extended by the results of this work, therefore provide an novel approach to probe related new physics.

Figure 1

The left and right panel show the constraint on $\alpha$ and $\beta /H_{*}$ in the range $T_{*}\sim {10}^{-6}-{10}^3\mathrm{GeV}$, respectively, where we set $\beta /H_{*}=10$ (left) and $\alpha =0.2$ (right). The solid gray line and the dot-dashed gray line represent the current constraint from the upper bound of stochastic GW background [22] and big bang nucleosynthesis [60], respectively.

Figure 2

The excluded parameter spaces of $\alpha$ and $\beta /H_{*}$ obtained from each constraint on ${\mathcal{P}}_{\mathcal{R}}(k)$.